Arno Lehmann wrote:
> Hi,
> 
> 05.09.2008 03:24, Jose Ildefonso Camargo Tolosa wrote:
> 
>>Hi!
>>
>>On Fri, Sep 5, 2008 at 4:17 PM, Ryan Novosielski <novosirj AT umdnj DOT edu> 
>>wrote:
>>
>>>-----BEGIN PGP SIGNED MESSAGE-----
>>>Hash: SHA1
>>>
>>>This is why I said that you'll almost always be shoeshining without
>>>spooling. Many modern drives are so fast that you theoretically need to
>>>have perfect conditions to avoid shoe-shining. Though, I suppose if
>>>you're streaming a LOT of data, you're OK.
>>>
>>>I wonder how many drives do variable speed writing.
> 
> 
> As far as I know, all current-technology drives that can write really 
> have that feature. All the LTO drives I read the specs on do, at least.
> 
> The range of speeds they can use vary a bit, though.
> 
> 
>>I wonder *how* the tape tells that it have to reduce its speed,
> 
> 
> When the buffer in the tape drives runs out of data. Essentially the 
> drive is capable to measure the speed with which data is fed to it and 
> tries to adjust speed accordingly.
> 
> 
>>I
>>think that bacula should instruct it to reduce its speed as part of
>>the configuration (similar as how a cd-r drive modifies its speed
>>*before* starting the write process).
> 
> 
> No, this is not something you can set from a user program. The vendor 
> tools might be able to do so, but the automatic speed adaption is 
> reliable enough to simply use it and don't worry about it.
> 
> 
>>>John Huttley wrote:
>>>
>>>>To follow up, LTO drives are very fast and this can be a liability.
>>>>However some drives, notably those by HP and some models by Tandberg support
>>>>variable speed writing. Normally down to 50% of normal.
>>>>These are resistant to shoe shining even without spooling.
> 
> 
> I would rather say they are *more* resistant to shoe-shining - if your 
> drive can write up to 150 MB/s and throttle down to 80 MB/s you will 
> still see shoe-shining if you only get backup throughput of 50 MB/s.
> 
> Arno

Its starting to look like slower drives may mean faster backups
in some cases...

Terry

-------------------------------------------------------------------------
This SF.Net email is sponsored by the Moblin Your Move Developer's challenge
Build the coolest Linux based applications with Moblin SDK & win great prizes
Grand prize is a trip for two to an Open Source event anywhere in the world
http://moblin-contest.org/redirect.php?banner_id=100&url=/
_______________________________________________
Bacula-users mailing list
Bacula-users AT lists.sourceforge DOT net
https://lists.sourceforge.net/lists/listinfo/bacula-users